The present disclosure relates to a pump and clutch assembly for use in a power transmission assembly. More particularly, a driven pump component of a fluid pump is coupled to a rotary drive member of the power transmission assembly by a radial friction clutch that is operable to limit the power consumed by the fluid pump.
Power transmission devices such as motor vehicle automatic transmissions, transfer cases and drive axles are often equipped with rotating shafts, bearings and/or gear sets contained within suitable housings. To achieve a desired operation of the various mechanical power transmitting components, it may be desirable to provide a lubricating fluid flow within the housing.
At least one known transfer case utilizes a fluid pump driven by a rotatable input member to draw lubricating fluid from a low-pressure sump and output pressurized fluid to another location within the housing. Pressurized lubricating fluid may be directed to one or more of the mechanical interfaces between the various components. Alternatively, pressurized fluid may be directed to a portion of the housing furthest from the ground to allow gravity to assist in disbursing the lubricating fluid.
While the prior designs may have achieved the primary goal of providing fluid flow, improvements may be made. For example, current customer specifications require that various power transmission devices pass low-speed abuse tests. To achieve favorable test results, it may be desirable to size the lubrication system to provide a predetermined minimum volume flow rate of lubricating fluid at a low operating speed. It should be noted, however, that current pump designs provide increased flow as the operating speed increases. The energy required to operate the pump also increases as the operating speed increases. As such, the pumping losses during vehicle high-speed or highway operation may be significant. Furthermore, lubricating fluid cavitation may also exist at the high pump rotational speeds.
Accordingly, there may be a need to limit the power provided to a lubrication pump during high-speed power transmission device operation.